Application of immobilized horseradish peroxidase (HRP) in porous calcium alginate (ca-alginate) for the purpose of phenol removal is reported. The optimal conditions for immobilization of HRP in ca-alginate were identified. Gelation (encapsulation) was optimized at 1.0% (w/v) sodium alginate in the presence of 5.5% (w/v) of calcium chloride. Upon immobilization, pH profile of enzyme activity changes as it shows higher value at basic and acidic solution. Increasing initial phenol concentration results in a decrease in % conversion. The highest conversion belongs to phenol concentration of 2 mM. Investigation into time course of phenol removal for both encapsulated and free enzymes showed that encapsulated enzyme had lower efficiency in comparison with the same concentration of free enzyme; however the capsules were reusable up to four cycles without any changes in their retention activity. Increasing enzyme concentration from 0.15 to 0.8 units/g alginate results in gradual increase in phenol removal. The ratio of hydrogen peroxide/phenol at which highest phenol removal obtained is found to be dependent on initial phenol concentration and in the solution of 2 and 8 mM phenol it was 1.15 and 0.94 respectively. (C) 2008 Elsevier B.V. All rights reserved.